Railway traffic controlling apparatus



R. K. CROOKS RAILWAY TRAFFIC CONTROLLING APPARATUS Nov. 18, 1941.

Filed Nov. 16, 1940 Deooa'zhg Mans INVENTOR' Balp .Cpaoks. BY

HIS ATTORNEY Patented Nov. 18, 1941 T OFFICE RAILWAY TRAFFIC CONTROLLINGi APPARATUS Ralph K. Crooks, Sharpsburg, Pa., assignor to TheUnion-Switch & Signal Company, Swissvale, Pa., a corporation ofPennsylvania Application November 16, 1940, Serial No. 365,887 8-Claims.(Cl. 246-433) My invention relates to railway traffic controllingapparatus, and more particularly to train carried train controlapparatus responsive to coded current. i

Railway trafiic controlling apparatus responsive to coded energy iswell-known and train carried train control apparatus responsive to codedalternating track circuit currentis used. The track circuit customarilyincludes the track rails of a track section and the alternating currentsupplied thereto is coded by being periodicallyinterrupted' at apreselected rate. Such coded current has alternate on and ofi periods,

current flowing during each on period and no current flowing during eachoff period. The on and off code periods are ordinarily of equalduration. The current is coded at any one of several difierent coderates according to different traffic conditions, the code rates of 180,120 and 75 interruptions per minute being those commonly used to reflectclear, approach-medium and approach trafiic conditions, respectively.

A receiving circuit is mounted on the train in inductive relation to thetrack rails to receive an electromotive force in response to such codedrail current. The electromotive force thus picked up by the traincarriedreceiving circuit has the same frequency as that of thealternating current supplied to the track rails and is of the same coderate as that of'the rail current. The 1 electromotive force thuspickedup by the receiving circuit is used to control the operation of a codefollowing relay through the medium of an electron tube amplifier, suchrelay being operated at a rate corresponding to the code rate of therail current. i

The code followingrelay is used in turn to control the train controlapparatus through the medium of a decoding means which is selectivelyresponsive to the rate at which the code following relay is operated andhence in turn is selectively responsive to the code rate of the. railcurrent.

r A railwaytrain is commonly provided with a 32 volt source of directcurrent for supplying vided forthe train control apparatus. Such specialgenerator, or dynamotor or motor generator add-to the cost of theequipment and require maintenance. Low voltage electron tubes which aresatisfactorilyoperated by 32 volts are now available.

-Inview of the above'cited conditions, an ob- J'ect or my invention isthe provision in railway traffic controlling apparatus of novel andimproved amplifying means for control of a train carried code followingrelay in response to electromotive forces derived from coded alternatincurrentsupplied to the track rails.

Another feature of my invention is the provision of railway trafliccontrolling apparatus incorporatingnovel and improved means for con-'trol of the grid voltage of a train carried electron tube amplifier inresponse to an electromojtive force derived from coded alternatingcurrent flowing in the track rails.

Again, a feature of myinvention is the provisionof novel and improvedlow voltage electron tube amplifier for railway traffic controllingapparatus, andwherewith power is made available sufiicient for operationlowingrelay.

Still another feature of my invention is the of a standard codefolprovision of a novel direct current electron tube amplifier forrailwaytrafiic controlling apparaing unit is connected through therectifier to the train carried receiving circuit which is mounted ininductive relation to the track rails to receive an electromotive forcein response to coded alternating current supplied to the rails.

The alternating electromotive force picked up by such receiving circuitis hence rectified and unidirectionalcurrent ismade to flow in theresistor of the biasing unit and a direct voltage is de- 'veloped acrossthe terminals of that unit. The

time constant of such biasing unit is'such that the direct voltage thusdeveloped across its terminals during an on code period is substantiallyuniform throughout the on period but quickly dies" away at the beginningof the next ofi code period. That is, the direct voltage developedacross the biasing unit follows the envelope of arrangement, aseparategenerator may be pro- 55 the electromotive force picked up by thereceiving circuit. Both the heater and the plate circuits of theelectron tube are connected to the usual 32 volt train carried source ofcurrent. A current limiting resistor is included in the heater circuitand is disposed in the lead from the cathode of the tube to the negativeterminal of the current source. The plate circuit includes the primarywinding of an output transformer and a condenser in multiple and thecurrent limiting resistor of the heater circuit. Thus there is developedacross this current limiting resistor a voltage drop derived from theheater circuit and the plate circuit currents flowing therethrough. Thevoltage drop due to the heater circuit current is of a relatively largevalue and of a given fixed value. That due to the plate circuit currentis of a relatively small value and for the purpose of this applicationcan be neglected.

A grid circuit including the biasing unit and the current limitingresistor is connected across the control grid and. cathode of theelectron tube. The biasing unit is poled so that the voltage developedacross its terminals due to the rectification of the electromotiveforces picked up from the rail current opposes the voltage drop in thecurrent limiting resistor. Hence the control grid of the electron tubeis provided with a fixed negative grid bias voltage equal to the voltagedrop in the current limiting resistor and this fixed bias voltage isvaried according to the voltage developed across the biasing unit, withthe result that the plate circuit current is varied according to thecode rate of the electromotive force picked up by the receiving circuit.

A code following relay is connected to the secondary winding of theoutput transformer. The condenser connected in multiple with the primarywinding of the output transformer is effective to by-pass variations ofthe plate circuit current of a frequency of the order of the frequencyof the alternating track rail current, but is ineffective to by-passvariations of the plate circuit current corresponding to the code rateof the track rail current. The code following relay is a polar relay andis operated in the usual manner by the electromotive force induced inthe secondary winding of the output transformer in response tovariations of the plate circuit current corresponding to the code rateof the track rail current.

The rectifier on the train may be any suitable type and preferably is adiode or a copper oxide rectifier. Ifv a copper oxide rectifier is usedthen a stage of amplification is preferably interposed bodying myinvention, and shall then point out the novelfeatures thereof in claims.

In the accompanying drawing, Figs. land 2 are diagrammatic views,showing two different forms of apparatus, each of which embodies myinvention. In the different views, like reference characters are used todesignate similar parts.

Referring to Fig. .1, the reference characters la and lb designate thetrack rails of a railway.

",5;hese rails. la, and lb would be formed by the chance at cycles persecond.

usual insulated rail joints, not shown, into consecutive track sections,and the rails of each such section would be supplied at times with codedalternating current. In order to better understand my invention, thealternating current will be considered as being of 100 cycles per secondsince such frequency is widely used in railway traffic controllingapparatus of the type here involved. It is to be understood, however,that my invention is not limited to alternating current of 100 cyclesper second, as current of other frequencies may be used. The trackwayapparatus for supplying coded current to rails la and lb is not shownsince it forms no part of my invention and may be any one of severalwell-known arrangements. Such trackway apparatus may, for example, bethat disclosed by Letters Patent of the United States No. 1,986,679,granted January 1, 1935, to L. V. Lewis, for Railway traffic controllingapparatus, and it is sufficient for the present application to point outthat the track rails la. and lb of Fig. 1 are supplied with alternatingcurrent coded at the code rates of 180, and 75 cycles per minute inresponse to clear, approach-medium and approach trafic conditions,respectively.

Two inductors 2 and 3 are mounted on a train in inductive relation torails la and lb, respectively. Inductors 2 and 3 are connected to areceiving circuit which also includes a condenser 4 and the primarywinding 5 of a transformer Tl. A condenser 6 is connected across asecondary winding 1 of transformer TI, and the receiving circuittogether with transformer Tl are tuned to resonance at the frequency ofthe alternating current and in the case here assumed for illustrationthey are tuned to res- It follows that an electromotive force appearsacross the terminals of secondary winding 1 and condenser 6 in responseto each on period of the coded rail current, and the electromotive forcequickly dies away at the beginning of each off period of the railcurrent. Such electromotive force is an alternating electromotive forceof 100 cycles per second and is coded at a code rate corresponding tothe code rate of the rail current.

A rectifier in the form of an indirect heated diode tube DT is mountedon the train. Tube DT is provided with a plate 8, a cathode 9 and afilament Ill. The filament ID of tube DT is heated by being connectedacross the terminals B32 and N32 of a current source TB, a currentlimiting resistor 62 being preferably interposed in the circuit. As hereshown the current source TB is a battery and preferably this battery isthe usual 32 volt battery carried on the train for supplying power tothe usual train lighting circuits.

A biasing unit BU consisting of a resistor l2 and a condenser inmultiple is provided. The biasing unit BU is included in a circuit whichcan be traced from the left-hand terminal of unit BU over secondarywinding 1 of transformer Tl and condenser 6 in multiple, plate 8 of tubeDT, intervening tube space to cathode 9 and ,to the right-hand terminalof unit BU.

The diode tube DT functions to rectify the alternating electromotiveforce appearing across across resistor l2- and hence a, direct voltageof I l6 and a filament 11.

nearly the peak voltage of the electromotive force is developed acrossthefterminals of unit BU, the

polarity of such direct voltage beingthat indicated by the plus andminus signs placed at unit BU; The time constant ofuthe circuitincluding resistorl2 and condenser II is such that the voltage thusdeveloped across the terminals of the unit BUduring an on code, periodof the electromotive force does not die away between the successivecycles of the electromotive force but quickly dies away during the nextoff period of the electromotive force. It follows that the directvoltage developed across, the unit BU substantially follows the envelopeof the rectified electrothe primary winding I and indirectly instep withthe on and off periods of the coded rail current. The control effectedby such direct voltage will shortly appear; I.

A low voltage electron tube TT is also mounted on the train. Tube TT maybe of any one of several types and may be a'tetrode having a plate l3,,acathode M, a control grid l5, another grid Tube TT is heated by itsfilament I! being connected across terminals B32 and N32 of thecurrentsource, a current limiting resistor I8 beingdisposed in the lead betweenthe negative side of filament I1 and the negative terminal of thecurrent source. Another grid 16 is connected to the positive terminal offilament ll and the cathode I4 is connected to the negative terminal offilament H as is customary for such electron tubes. Hence currentlimiting resistor I8 is disposed in the lead between cathode l4 and thenegative terminal N32 of the current source.

Tube TT is provided with a grid circuit that can be traced from controlgrid l5 over wire l9, biasing unit BU and current limiting resistor 18to cathode M. It is clear that the .voltage drop in resistor l8 causedby the heater circuit current provides a fixed negative grid biasvoltage for the tube 'IT. Also the direct voltage developed. acrossbiasing unit BU in the manner explained hereinbefore opposes the voltagecreated across resistor l8 and a resultant grid bias voltage is created.Inother words, the

normal fixed negative grid bias voltage for tube TT is varied by thevoltage developed across unit BU due to the rectified electromotiveforce picked up from the track rails and the grid voltage is variedsubstantially in step with the on and off code periods of the railcurrent.

i A plate circuit for tube TT is formed from positive terminal B32 ofbattery TB over primary winding 20 of output transformer T2. in

multiple with a condenser 2|, plate I3 of tube TT, intervening tubespace to cathode l4 and current limiting resistor IE to negativeterminal N32. Since the voltage developed across unit BU decreases thenegative bias voltage for control grid 15, the plate circuit current iscorrespondingly increased during each on code period. Hence the averagevalue of the plate circuit current is varied substantially in step withthe code period of the. received electromotive to secondary winding 22of transformer T2, the

arrangement beingsuch that contact member coding means.

23 of relay MS is operated to the left-hand position as viewedin Fig. 1to engage normal contact 24" when an electromotive force is induced insecondary winding 22 due to an increase of the plate circuiti current,and contact member 23 is operated to-the right-hand position to engagereverse contact 25 in response to the elec-.- tromotive force induced insecondary winding 22 when the average value of the plate circuit currentis decreased. i Operation of contactmember 23 of relay MS to alternatelyengage" contacts 24 and- 25, causes direct current from battery TB to bealternately supplied to the two portions of the primary winding 26- ofa: decoding transformer T3 whose secondary-winding 21 is connected tothe input terminals of a decoding means DM. Thus with relay MS operatedan alternating electromotive-force is induced in secondary winding 2! ofdecoding transformer T3 and applied to the decodingmeans DM, thefrequency of such electromotive force corresponding to the rate at whichrelay MS is operated.

The decoding means DM may take any one of several well-known forms andmay be the tuned circuit arrangement covered by Letters Patent of theUnited States No. 1,773,515, granted August 19, 1930, to C. C, Buchanan,for Railway traffic controlling apparatus. It is sufficient for theinstant application to point out that control relays A, R and Lconnected to the output side of decoding means DM are selectivelycontrolled according to the frequency of the electromotive force appliedto the input terminal of the de- As here shown relays A and L areeffectively energized and picked up when decoding means DM is suppliedwith electromotive force of a frequency created by operation ofrelay MSat a rate correspondingto the 180 code rate of the track rail current.Relays R and L are effectively energized and picked up. and relay A isreleased when decoding means DM is supplied with an electromotive forceof a frequency created by operation of relay MSat a rate correspondingto the code rate of the rail current, and relay L is effectivelyenergized and picked up and relays A and R arereleased when decodingmeans DM is supplied with, an electromotive force of a frequencycorresponding to operation of relay MS at the '75 code rate of the railcurrent. Furthermore, all three control relays A, R and L are releasedwhen code following relay MS is inactive. f

Control relays A, R and L are used to control the operating circuits ofa train control means,

here shown as a cab signal CS, signal CS being.

a four-position color light signal. The operating circuits are thosecommonly employed and as here shown when relay A is picked up closingfront contact 28 an operating circuit easily traced is completed forlamp 29 and that lamp is illuminated to cause the signal CS to display aclear signal indication. When relay A is released closing back contact30 and relay R is picked up closing front contact .31, an operatingcircuit is formed for lamp. 32 and that lamp is illuminated to causesignal CS to display an approach-medium indication. When relays A and Rare released, closing back contacts 30. and 33,

respectively, and relay.L is picked up to close front contact, anoperating circuit is formed for lamp 35 and that lamp is illuminated tocause signal CS to display an approach signal indication. When relays A,R and L are released, closing back contacts 30, 33 and 36, respectively,an

operating circuit is formed from lamp 31 and that lamp is illuminated tocause signal CS to display a slow speedsignal indication.

In describing the operation of the apparatus of Fig. 1, it is to beobserved that normally the electron tube TT is provided with a fixednegative grid bias voltage clue to the voltage drop across currentlimiting resistor l3 and current of a steady given value flows in theplate circuit. I shall assume that current coded at the 180 code rate issupplied to rails la and lb to reflect clear trafiic conditions. Underthis condition an alternating' electromotive force of the 180 code rateis picked up by the receiving circuit and made to appear acrosssecondary winding 1 of transformer- TI. This-alternating electromotiveforce is rectified by diode tube DT and unidirectional current flows inresistor l2 of the biasing unit DU so that adirect voltage nearly equalto the peak value-of the electromotive force picked up by the receivingcircuit is developed across the terminals of the unit BU. This directvoltage across unit BU remains substantially uniform in value during theon periodof the coded current but quickly dies away at the start of thefollowing 01f code period due to the time constant of the unit. That isto say, the direct voltage across unit BU follows-the envelope of theelectromotive force picked upby the receiving circuit. The voltagedeveloped across unit BU opposes the voltage 3 drop through resistor l8and consequently causes the grid I of tube TT to be less negative inpotential with respect tothe cathode 14 during each on code period.Hence the average value oft-he plate circuit current is increased duringeach on code period. Such increase in the average value of the platecircuit current induces in secondary winding 22 of output transformer T2an electromotive force of a polarity as required to operate relay MSto'its left-hand position. At the start of the following off codeperiod, the voltage of unit BU dies away and the biasing voltage of tubeTT returns to its normal fixed value so that the plate circuit currentdecreases to its given normal value. average value of the plate circuitcurrent induces in secondary winding 22 an electromotive force of apolarity opposite to that induced when the plate circuit increased andrelay MS is operated to-its right-hand position. Since the rail currentis of the 180 code rate, the code following relay MS is operated at acorresponding code rate and as pointed out hereinbefore, the controlrelay A is eifectively energized and pickedup in response to suchoperation of the code following relay and lamp 29 is illuminated causingsignal OS to display a clear signal indication.

It is to be seen therefore that the value of the current fiowing in theplate circuit of tube TT is in accordance with the envelope of thealternating electromotive force picked up by the receiving circuit, andcode following relay MS is operated in the usual manner withsubstantially equal on and oil periods. Since the alternatingelectromotive force picked up by the receiving circuit is rectified andunidirectional current fiows in resistor l2 of the biasing unit. whichin turn causes a direct voltage to be developed across the terminals ofthat unit, it follows that tube TT of Fig. 1 functions as direct'currentamplifier, amplifying the direct current flowing in resistor l2 of thebiasing unit.

When current coded at either the 120 or '75 code rate issupplied to thetrack rails la and lb,

Y the. operation of the apparatus of Fig. 1 is the This decrease in thesame except for the fact that the code following relay MS- is operatedat a rate corresponding either to the 120 or code rate of the railcurrent and such operation of relay MS in turn controls the controlrelays so that relay R is picked up for the code rate to cause thedisplay of the approach medium signal lamp 32, and relay L only ispicked up in response to the 75 code rate to cause the display ofapproach signal lamp 35.

It is to be pointed out that in the event no current issupplied to thetrack rails and no electromotivcforce ispicked up by the receivingcircuit, then the normalfixed bias voltage for tube TT prevails and thegiven steady value of direct current flows so that no transfer of energyis effected in transformer T2 and relay MS is inactive causing relays A,R and L to be all released so that the slow speed signal lamp 3! isilluminated.

Referring to Fig. 2, the diode rectifier tube DT of Fig. l is replacedby a copper oxide rectifier CR and. a stage of amplification including alow voltage electron tube FT is inserted between the rectifier CR andthe train carried receiving circult.

Electron tube FT is preferably of the same type as tube TT. The filament44 of tube FT is heated by being connected across battery TB through acurrent limiting resistor 45, cathode 4| is connected to the negativeend of filament 44 and grid 43 is connected to the positive end of thefilament. The grid circuit for tube FT includes control grid .42, a gridleak condenser unit GL, secondary winding 1 of transformer TI andcondenser 6 in multiple, and the upper portion of resistor 4-5 tocathode 4!. The plate circuit of tube FT includes the positive terminalB32 of the current source, primary winding 46 of transformer T4, plate40 of tube FT, intervening tube space to cathode id and current limitingresistor 45 to the negative terminal N32. The secondary winding 41 oftransformer T4 is connected to the input terminals of rectifier CR andthe output terminals of rectifier CR are connected across the biasingunit BU which consists of resistor l2 and condenser l l the same as inFig. 1.

It is clear that the alternating electromotive force appearing acrossthe secondary Winding 1 of transformer Tl due to the coded rail currentis amplified by tube FT and analternating electromotive force is appliedto the rectifier CR and rectified to cause unidirectional current toflow in resistor l2 of unit BU. This current flowing in resistor l2develops a direct voltage across the terminals of the unit BU in thesame manner as described in connection with Fig. 1.

The grid circuit for tube TT of Fig. 2 is similar to that described inFig. 1 and includes control grid l5, biasing unit BU, current limitingresistor 45 and cathode M. It is to be observed that the unit BU of Fig.2 is disposed so that the voltage developed across the unit opposes thenegative voltage which is created across resistor 45 due to the heatercurrents of tubes FT and TT flowing therethrough.

The plate circuit for tube TT, master relay MS, decoding means DM,control relays A, R and L, cab signal CS and the circuit associatedtherewith are the same in all respects to those described in Fig. l andthe description thereof need not be repeated.

It is clear that the apparatus of Fig. 2 will operate in substantiallythe same manner as the apparatusof Fig. 1 in response to codedalternatpicked up by the receiving circuit is firstamplified at tube FTbefore it is applied to the input terminals of the rectifier. Also therectifier CR of Fig. 2 is a full wave rectifier Whereas the di-' poweras applied to the rectifier, and hence as applied to the code followingrelay MS for operation thereof throughout the usual range of nor-- malto maximum value of rail current and code distortion is avoided, Thisfeature however is no part of my present invention. 1

It is apparent, therefore, that Ihave provided two forms of novel andimproved low voltage electron tube amplifiers foruse with train carriedtrain control apparatus. 3

Although I have herein shown and described only two forms of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of, my invention. i

Having thus described my invention, what I claim is: V 1 1. In railwaytraffic controlling apparatus for use with a receiving circuit mountedone train in inductive relation to the track rails to receive inresponse to coded alternating current supplied to the. railsall-electromotive force having an envelope substantially in step withthe on and ofifperiods of the coded current, the combination comprising,a train carried biasing unit in-', cluding a resistor and a condenserinmultiple, a train carried rectifier, a circuit including saidrectifierto couple said biasing unit to saidreceiving circuit to causeunidirectional current to fiow in the resistor of saidunit and a directvoltage to be developed across said biasing unit in response to saidreceived electromotive force, said biasing unit constructed to have apredetermined time constant to cause saiddirect voltageto substantiallyfollow the envelope of said received electromotive force; a traincarried electron tube having a plate, a cathode and a control grid; agrid circuit including said biasing unit connected across said controlgrid and said cathode to control the potential of the grid with re spectto said cathode by said direct voltage a plate circuit including asource .of current and a winding connected across said plate andcathode, and a code following relay coupled to said plate circuitwinding effectivelyoperated by the variations of the plate circuitcurrent in response to such controlof the potential of the grid withrespect to the cathode. a 5 2. In railway traffic controlling apparatusfor usewith a receiving circuit mounted on a train in inductive relationto the track rails to receive an alternating electromotive force inresponse to alternating current coded at a given code rate suppliedtothe'rails, the combination comprising, a train carried biasing unitincluding a resistor and a condenser in multiple, a train carriedrectifier; a circuit including said rectifier, said biasing unit andawinding coupled toqsaid receiving circuit to cause a direct current ofsaid code rate to flow in the resistor of said unit; a train carriedelectron tube having a plate, a cathode and alcontrol grid; 9. gridcircuit including said biasing unit connected across the control gridand cathode of said. tube, a plate circuit including a current sourceand a Winding connected across the plate and cathode ofsaid tube, and acode following relay coupled to said plate circuit winding effectivelyoperated at said code rate due to the amplification of the directcurrent flowing in the resistor of said biasing unit as effected bysaidelectron tube.

3. In;railway trafiic controlling apparatus for use :With a receivingcircuit mounted on a train in inductive relation to the track rails toreceive an electromotive force in response to coded alternating currentsupplied to the rails, the combination comprising, a'train carriedbiasing unit including a resistor and a condenser in multiple, a traincarried rectifier, a circuit including said rectifier and awindingcoupled to said receiving circuitconnectedxto said biasing unitto develop a direct voltage across the terminals of said biasing unit inresponse to such received electromotive force; a train carried electrontube having a platega cathode and a control grid; a heater circuitincluding-a circuit source and a current limiting-resistor for said tubeand having said current limiting resistor disposed between saidcathodeand the negative terminal of the current source, a grid circuitincluding said biasing unit and. said current limiting resistorconnected across said ,control grid and cathode, -said biasing unitpoled to cause the voltage developed across its termi nals to oppose theVoltage drop occurring across said current limiting resistor to controlthe grid voltage each on period of said coded current, a plate circuitincluding a currentsource and a windingconnected across the plateandcathode'of said tube, and a'code following relay coupled to said platecircuit winding effectively operated by the variations of the plate.circuit current. caused by such control of the grid voltage. I s

4. In railway traffic controlling apparatus for use witha receivingcircuit mounted 'on'a train in inductive relation to the track" rails to.receive an electromotive .force in response to coded alternatingcurrent supplied to the rails, the combination comprising, a traincarried biasing unit including a resistorTand a condenser in multiple, atrain carried rectifier, means includ ing said rectifier to connect saidbiasing unit to a Winding coupled to said receiving circuit tocauseunidirectional current to fiow in the resistor of said unit anddevelop a direct voltage across. the terminals of the unit in responseto said received electromotive force; a train carried electron tubehaving a plate, a cathode and a control grid; a grid circuit connectedacros's said control grid and cathode and including said biasi'ng unitand another biasing means, said biasing means effective to provide.

a predetermined negative grid bias voltage and said biasing unit poledto cause the voltage developed across its terminals to oppose saidpredetermined bias voltagetocontrol the grid voltage in response tosaid-coded rail current, a plate circuit for said tubeand including awinding and, a :current I source, and' a code following relay coupled tosaid plate circuit Winding effectively operated by the variations oft'heplate circuit current caused by such control of the grid voltage;

5. In railway traffic controlling apparatus for use with a'receivingcircuit mounted on a train in inductive relation to the track rails toreceive an electromotive force in response to alternating current codedat a given code rate supplied to the rails, the combination comprising,a train carried biasing. unit including a resistor and a condenser inmultiple, a train carried rectifier, means including said rectifier toconnect said biasing unit to a winding coupled to said receivingcircu'itto cause unidirectional current to flow in the resistor of saidunit and develop a direct voltage across the terminals of the unit inresponse to .said received electromotive force; said biasing unithav'inga time constant effective to cause the voltage developed acrosssaid unit to substantially follow'the envelope of said receivedelectromotive force; a train carried electron tube having a plate, acathode and a control grid; a grid :circuit connected across saidcontrol grid and cathode and including said biasing. unit and anotherbiasing means, said biasing means effective to provide a predeterminedfixed grid bias voltage and said biasing unit disposed to cause thevoltage developed across the unit to oppose said fixed bias voltage tocause a variation in the potential of the grid with respect to thecathode to vary substantially in step with the on and off periods ofsaid received electromotive force, a plate circuit connected across theplate and cathode of said tube and including a winding and a currentsource, and a code following relay coupled to said'platecircuit windingto opera ate the relay: in IIESDODSG to the variations of the platecircuit caused by said variation of the potential of the grid withrespect to the cathode.

6. In railway traflic controlling apparatus for use with a receivingcircuit mounted on a train in inductive relation to the track rails toreceive an electromotive forcein response to alternating current codedat a given code rate supplied to the rails, the combination comprising,-a train carried biasing unit including a resistor and a condenser inmultiple, a train carried rectifier, means including said rectifier toconnect said biasing unit to a winding coupled to said receiving circuitto cause unidirectional current to flow in the resistor of said unit anddevelop a direct voltage across the terminals of the unit in response tosaid received electromotive force; a train carried 32 volt electron tubehaving a plate, a cathode and a control grid, 9, train carried 32 voltsource of direct current, a heater circuit for said tube including saidsource and a current limiting resistor with the resistor disposedbetween said cathode and the negative terminal.

of the current source, a grid circuit connected across the control gridand cathode and including in series said biasing. unit and said currentlimiting resistor, said biasing unit disposed to cause the voltagedeveloped across its terminals to oppose the voltage drop in saidcurrent limitingresistor to Vary the potential of the grid with respectto the cathode in step with the on and off :periods of the receivedelectromotive force, a plate circuit to connect said 32 volt source ofcurrent acrossthe plate and cathode of the tube, a code followingrelay,and a transformer having a primary winding interposed in said platecircuit and a secondary winding connected to said icod'e folowing relayto operate the relay by the variations :of the plate circuit currentcaused by said variations of the potential of the grid with respect tothe cathode.

'7. In railway traffic controlling apparatus for use with a receivingcircuit mounted on a train in inductive relation to the track rails toreceive an alternating electromotive force of a given code rate whenalternating current coded at said code rate'is supplied'to the rails,the combination comprising, a first and a second electron tube mountedon the train, a train carried biasing unit including a resistor and acondenser in multiple, a train carried rectifier, a first and a secondtransformer mounted on the train, a grid circuit for said first tube andincluding a winding coupled to said receiving circuit, a plate circuitfor said first tube and including a current source and a primary windingof said first transformer, means including said rectifier to connectsaid biasing unit to a secondary winding of said first transformer tocause direct current of said code rate to flow in the resistor of saidbiasing unit in response to said received electromotive force asamplified by said first tube, a grid circuit for said second tube andincluding said biasing unit, a plate circuit for said second tube andincluding a current source and a primary winding of said secondtransformer, and a code following relay connected to a secondary windingof said second transformer effectively operated at said code rate due tothe amplification of the direct current flowing in the resistor of saidbiasing unit as effected by said second tube.

8. In railway trafiic controling apparatus for use with a receivingcircuit mounted on a train in inductive relation to the track rails toreceive an alternating electromotive force of a given code rate whenalternating current coded at said code rate is supplied to the rails,the combination comprising, a first and a second electron tube mountedon the train, a train carried biasing unit including a resistor and acondenser in multiple, a train carried rectifier, a first and a secondtransformer mounted on the train, a train carried battery, a heatercircuit for said first tube connected to said battery, a heater circuitfor said second tube connected to said battery and including a currentlimiting resistor disposed in the lead between the cathode of that tubeand the negative terminal of said battery, a grid circuit for said firsttube and including a winding coupled to said receiving circuit, a platecircuit for said first tube and including said battery and a primarywinding of said first transformer, means including said rectifier toconnect said biasing unit to a secondary winding of said firsttransformer to develop a direct voltage across said biasing unit inresponse to each on period of said received electromotive force asamplified by said first tube, a grid circuit for said second tube andincluding said biasing unit and said current limiting resistor, a platecircuit for said second tube and including said battery and a primarywinding of said second transformer, and a code following relay connectedto a secondary winding of said second transformer effectively operatedat said code rate due to the grid voltage control of said second tube asefiected by said direct voltage developed across said biasing unit andthe voltage drop across said current limiting resistor caused by theheater current flowing therethrough.

RALPH K. CROOKS.

